Yearning to be a superhero isn’t the same thing as actually being one, but the two states aren’t nearly as far apart as they appear. When kids who read comic books imagine that they can leap tall buildings, spider-surf the air, or lay waste to bad guys with iron-chested daring, simply by dreaming of doing those things they already share something with the pop vigilantes on the page. They’ve become the equivalent of a superhero’s alter ego: the Bruce Wayne/Clark Kent ”ordinary guy” side — the side that covets and lives vicariously, that has to wear a costume and an attitude to fulfill his ”real” self. So when Dave Lizewski (Aaron Johnson), the 17-year-old hero of Kick-Ass, decides to put on a green jumpsuit with yellow piping and become a phantom crime-fighter, even though he has no special abilities or physical flair, we can see that he hasn’t taken leave of his senses. Dave, a brainy and bushy-haired geek who looks like Harry Potter crossed with the young Steven Spielberg, knows all too well that he’s got nothing going for him but will and desire — nothing but the drive to be a superhero. It’s as if he thought that the sheer power of suggestion could fool the bad guys, and himself along with them.

Kick-Ass, directed by Matthew Vaughn (Layer Cake), is an enjoyably supercharged and ultraviolent teen-rebel comic-book fantasy that might be described — in spirit, at least — as reality-based. When Dave, in costume, gets out into the world of grungy criminals, he discovers that putting a stop to evil is no picnic. A showdown with parking-lot thieves puts him in the hospital, and the fact that he bleeds real blood is part of what hooks you; the movie never makes it too easy for him. But it doesn’t mock him, either. Standing there in his silly/noble outfit, brandishing a pair of ninja batons, he looks just crazy enough to be a little scary, and when he chases off a pack of muggers and the exploit gets caught on video, it becomes a Web sensation. The legend of Kick-Ass is born.

Adapting the comic book by Mark Millar and John S. Romita Jr., Vaughn gets a lot of mileage out of the classic superhero tropes by converting them to Internet-age satire: ? a media firestorm over the mystery of Kick-Ass’ identity; Dave’s one-way flirtation with the gorgeous Katie (Lyndsy Fonseca), who thinks he’s her gay BFF. As for the other characters, they fill in a vibrant pop patchwork of kamikaze comic-book wish fullfilment. As Chris, a mobster’s son who tries to uncover Kick-Ass’ identity by becoming a superhero himself — the sports-car-driving Red Mist — Christopher Mintz-Plasse proves great at playing the comedy of aggression off against his spindly, mouth-breathing boyishness. And just when it looks as if Dave’s awkward valor is going to get him killed, along comes an even unlikelier masked do-gooder: Hit Girl, a pint-size, purple-haired martial-arts demon who’s like a prepubescent version of Uma Thurman in the Kill Bill films. Hit Girl’s real name is Mindy Macready (Chloë Grace Moretz), and unlike Dave and Chris, she’s a stylized figure out of an action-thriller dream. The film becomes a dialogue between the two poles: the normal-guy teens who long to be invincible, and the little girl who more or less is.

Hit Girl, trained by a daddy (Nicolas Cage) with rubber-suited-vigilante ambitions of his own, turns out to be the most ass-kicking character in the film. The reason that’s a good joke is that the way she turns villains into cannon fodder is really no more preposterous than, say, Bruce Willis doing the same thing. Yet is it a problem that Kick-Ass is by far the most violent movie ever to feature kids as heroes? Parents should consider themselves warned, though personally, I just wish that the film had ended up a bit less of an over-the-top action ride. It didn’t need this much slam-bang when it had us at real-life superheroics. B+